U.S. patent application number 11/519899 was filed with the patent office on 2007-06-28 for supercritical co2 cleaning system and method.
This patent application is currently assigned to Industrial Technology Research Institute. Invention is credited to Cheng-Chun Chen, Shing Chen, Jia-Ming Huang, Chuan-Hui Liu.
Application Number | 20070144555 11/519899 |
Document ID | / |
Family ID | 38192179 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070144555 |
Kind Code |
A1 |
Chen; Cheng-Chun ; et
al. |
June 28, 2007 |
Supercritical CO2 cleaning system and method
Abstract
A supercritical CO.sub.2 cleaning system is provided,
comprising: a closed high-pressure cleaning trough, which is a
funnel-shaped vessel tapered from top to bottom; a bearer platform,
located within the closed high-pressure cleaning trough and rotated
with respect to an object to be cleaned and used for bearing the
object to be cleaned; and a movable nozzle set, disposed within the
closed high-pressure cleaning trough and above the bearer platform,
wherein the object to be cleaned can be cleaned via the movable
nozzle set and impurity pollutants will be easily deposited at the
bottom of the closed high-pressure cleaning trough after cleaning.
A supercritical CO.sub.2 cleaning method is also provided,
comprising: providing a wafer or an object to be cleaned within a
closed high-pressure cleaning trough; introducing liquid CO.sub.2
into the closed high-pressure cleaning trough; adding co-solvents
and surfactants into the cleaning trough; activating a movable
nozzle set in order to increase the cleaning performance; rotating
the wafer or the object to be cleaned to remove the impurity
pollutants; and lowering the pressure to discharge the CO.sub.2 and
the impurity pollutants in order to clean the wafer or the object
to be cleaned.
Inventors: |
Chen; Cheng-Chun; (Tainan
County, TW) ; Chen; Shing; (Hsinchu County, TW)
; Liu; Chuan-Hui; (Hsinchu County, TW) ; Huang;
Jia-Ming; (Hsinchu City, TW) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE, FOURTH FLOOR
ALEXANDRIA
VA
22314
US
|
Assignee: |
Industrial Technology Research
Institute
HsinChu
TW
|
Family ID: |
38192179 |
Appl. No.: |
11/519899 |
Filed: |
September 13, 2006 |
Current U.S.
Class: |
134/1 ; 134/172;
134/184; 134/198; 134/34 |
Current CPC
Class: |
B08B 7/0021 20130101;
H01L 21/67051 20130101; H01L 21/02101 20130101 |
Class at
Publication: |
134/1 ; 134/172;
134/184; 134/198; 134/34 |
International
Class: |
B08B 3/12 20060101
B08B003/12; B08B 3/00 20060101 B08B003/00; B08B 6/00 20060101
B08B006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2005 |
TW |
94146613 |
Claims
1. A supercritical CO.sub.2 cleaning system, comprising: a closed
high-pressure cleaning trough, which is a funnel-shaped vessel
tapered from top to bottom; a bearer platform, located within said
closed high-pressure cleaning trough and rotated with respect to an
object to be cleaned and used for bearing said object to be
cleaned; and a movable nozzle set, disposed within said closed
high-pressure cleaning trough and above said bearer platform,
wherein said object to be cleaned can be cleaned via said movable
nozzle set and impurity pollutants will be easily deposited at the
bottom of said closed high-pressure cleaning trough after
cleaning.
2. The supercritical CO.sub.2 cleaning system as claimed in claim
1, wherein said bearer platform is titled with respect to the
horizontal plane with an angle formed therebetween, during the
cleaning, the impurity pollutants can easily and regularly flow
away from said object to be cleaned along the angle and reach the
bottom of said trough.
3. The supercritical CO.sub.2 cleaning system as claimed in claim
1, wherein said movable nozzle set is the combination of at least
one movable nozzle and at least one ultrasonic oscillator having
the frequency of 0.8 MHz.about.3.5 MHz, said ultrasonic oscillator
may form a module together with said movable nozzle, or said
ultrasonic oscillator is combined with said bearer platform by
mounting it above or beneath said bearer platform.
4. The supercritical CO.sub.2 cleaning system as claimed in claim
3, wherein said ultrasonic oscillator is convergent or
non-convergent, the ultrasonic body of said convergent ultrasonic
oscillator may form a concave or an additional horn-shaped nozzle
is provided in order to achieve the convergence, such that when the
supercritical CO.sub.2 flows into said closed high-pressure
cleaning trough, it can inject out via said movable nozzle and
perform an ultrasonic cleaning.
5. The supercritical CO.sub.2 cleaning system as claimed in claim
3, wherein said ultrasonic oscillator is disposed at a suitable
angle with respect said object to be cleaned, such that the
impurity pollutants on said object to be cleaned can easily and
rapidly leave away.
6. The supercritical CO.sub.2 cleaning system as claimed in claim
3, wherein the operation conditions are as follows: the operation
temperature is between 15.degree. C..about.150.degree. C., the
operation pressure is between 50.about.250 atm, and the operation
frequency range of the ultrasonic set is between 0.8 MHz.about.3.5
MHz.
7. The supercritical CO.sub.2 cleaning system as claimed in claim
3, wherein within said movable nozzle set, the ultrasonic
oscillator pipes, the movable nozzle pipes, and the bearer platform
pipes are embedded within a high-pressure tube, such that a second
pollution on said object to be cleaned can be avoided.
8. The supercritical CO.sub.2 cleaning system as claimed in claim
3, wherein said object to be cleaned is a wafer, low-k material, or
MEMS.
9. A supercritical CO.sub.2 cleaning method comprising: providing a
wafer or an object to be cleaned within a closed high-pressure
cleaning trough; introducing liquid CO.sub.2 into said closed
high-pressure cleaning trough; adding co-solvents and surfactants
into said cleaning trough; activating a movable nozzle set in order
to increase the cleaning performance; rotating said wafer or said
object to be cleaned to remove the impurity pollutants; and
lowering the pressure to discharge the CO.sub.2 and the impurity
pollutants.
10. The supercritical CO.sub.2 cleaning method as claimed in claim
9, wherein after the CO.sub.2 and the impurity pollutants are
discharged, another cleaning can be performed by fresh CO.sub.2,
and said wafer or said object to be cleaned can be taken out after
this another cleaning.
11. The supercritical CO.sub.2 cleaning method as claimed in claim
10, wherein said wafer or said object to be cleaned is titled with
respect to the horizontal plane with an angle formed therebetween,
during the cleaning, the impurity pollutants can be easily and
regularly discharged.
12. The supercritical CO.sub.2 cleaning method as claimed in claim
10, wherein said movable nozzle set is the combination of at least
one movable nozzle and at least one ultrasonic oscillator having
the frequency of 0.8 MHz.about.3.5 MHz, said ultrasonic oscillator
may form a module together with said movable nozzle by mounting it
above or additionally underneath said object to be cleaned in order
to increase the cleaning performance.
13. The supercritical CO.sub.2 cleaning method as claimed in claim
12, wherein said ultrasonic oscillator of said movable nozzle set
is disposed at a suitable angle with respect said object to be
cleaned, such that the impurity pollutants on said object to be
cleaned can easily and rapidly leave away.
14. The supercritical CO.sub.2 cleaning method as claimed in claim
3, wherein the operation conditions are as follows: the operation
temperature is between 15.degree. C..about.150.degree. C., the
operation pressure is between 50.about.250 atm, and the operation
frequency range of the ultrasonic set is between 0.8 MHz.about.3.5
MHz.
15. The supercritical CO.sub.2 cleaning method as claimed in claim
12, wherein said object to be cleaned is a wafer, low-k material,
or MEMS.
16. The supercritical CO.sub.2 cleaning method as claimed in claim
12, wherein the cleaning can be performed in conjunction with the
micro-emulsification technology by adding co-solvents, surfactants
and chelating agents in order to increase the cleaning
performance.
17. The supercritical CO.sub.2 cleaning method as claimed in claim
12, wherein the work range of said movable nozzle set covers the
whole surface of said object to be cleaned, such that said object
to be cleaned can be uniformly cleaned.
18. The supercritical CO.sub.2 cleaning method as claimed in claim
12, wherein the respective working ranges of a plurality of
ultrasonic waves and a plurality of nozzles in said movable nozzle
set overlap with one another, such that any uncleaned areas can be
avoided.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a supercritical CO.sub.2
cleaning system and method, and more particularly to a
supercritical CO.sub.2 cleaning system and method for cleaning an
object to be cleaned located on a bearer platform in a closed
high-pressure cleaning trough.
[0003] 2. Description of the Related Art
[0004] In traditional cleaning processes for wafers or elements, a
lot of super pure water and chemical solvents are needed to remove
nanopollutants on the surface of a wafer or element. At the same
time, a lot of waste solvents will be treated. In a nanoprocess (65
nm) or a more complex process, the pollutants in nanoholes in the
trenches and the high aspect ration structures of a wafer or
element can not be efficiently cleaned due to the limit of the
liquid surface boundary layer.
[0005] In past technologies, wafers or elements can be cleaned by
ozone water, however, these wafers or elements are stationary and
unable to be rotated. Furthermore, these wafers or elements have to
be cleaned in conjunction with a MHz class ultrasonic wave and
dried by high-pressure CO.sub.2. In another technology, wafers or
elements can be cleaned by water in conjunction with an ultrasonic
wave having a frequency of 900.about.1,100 KHz. It is noted that,
the ultrasonic wave apparatus is provided outside the cleaning
trough, but the cleaning time and efficiency still needed to be
improved.
[0006] The above methods for cleaning elements such as wafers by
ozone water or water are gradually replaced by new technologies,
for example supercritical fluid matters. A supercritical fluid
matter has physical properties between those of a gaseous matter
and a liquid matter. The viscosity of a supercritical fluid matter
is close to that of a gaseous matter, and the density of a
supercritical fluid matter is close to that of a liquid matter. For
its higher density, more supercritical fluid matters can be
transported than gaseous matters. For its lower viscosity, the
power needed for transporting a supercritical fluid matter is lower
than that of a liquid matter, that is, the mass transport
resistance of a supercritical fluid matter is much lower than that
of a liquid matter such that the mass transport of a supercritical
fluid matter is faster than that of a liquid matter. Additionally,
similar to a gaseous matter, a supercritical fluid matter has
nearly no surface tension, such that it can easily permeate into a
porous texture.
[0007] In addition these physical properties, a supercritical fluid
matter also has different chemical properties from a gaseous matter
and a liquid matter. For example, CO.sub.2 does not have any
extraction capability in gaseous state, however, after entering the
supercritical state, it will become organophilic and therefore
capable of dissolving organic matters. The dissolving capability
will vary with the temperature and the pressure. A supercritical
CO.sub.2 has the properties of low surface tension, low viscosity,
and high diffusibility, such that it can easily diffuse into
nanoholes, thereby it can be used for a dry cleaning process and
reduce the waste of water resource. Accordingly, it is a potential
.left brkt-top.Green Cleaning and Producing Technology.right
brkt-bot..
[0008] However, as to the current supercritical CO.sub.2 cleaning
system and method, a simple, convenient, and efficient
supercritical CO.sub.2 cleaning system is still needed such that
the cleaning time can be reduced.
SUMMARY OF THE INVENTION
[0009] It is one object of the present invention to provide a
supercritical CO.sub.2 cleaning system and method for increasing
the cleaning efficiency and shortening the cleaning time.
[0010] To achieve the above purposes, a supercritical CO.sub.2
cleaning system of the present invention comprises: a closed
high-pressure cleaning trough, which is a funnel-shaped vessel
tapered from top to bottom; a bearer platform, located within the
closed high-pressure cleaning trough and rotated with respect to an
object to be cleaned and used for bearing the object to be cleaned;
and a movable nozzle set, disposed within the closed high-pressure
cleaning trough and above the bearer platform, wherein the object
to be cleaned can be cleaned via the movable nozzle set and
impurity pollutants will be easily deposited at the bottom of the
closed high-pressure cleaning trough after cleaning, furthermore
the cleaning performance is increased in conjunction with
co-solvents, surfactants, and chelating agents and the cleaning
time is shortened in conjunction with micro-emulsification
technology.
[0011] Additionally, to achieve the above purposes, a supercritical
CO.sub.2 cleaning method of the present invention comprises the
following steps: providing a wafer or an object to be cleaned
within a closed high-pressure cleaning trough; introducing liquid
CO.sub.2 into the closed high-pressure cleaning trough; adding
co-solvents and surfactants into the cleaning trough; activating a
movable nozzle set in order to increase the cleaning performance;
rotating the object to be cleaned to remove the impurity
pollutants; and lowering the pressure to discharge the CO.sub.2 and
the impurity pollutants. Additionally, suitable co-solvents,
surfactants, and chelating agents can also be used to push the
supercritical CO.sub.2 into a steady and homogenous state and
increase the polarities of the CO.sub.2 in order to bring its
cleaning performance into full play, the suitable combination can
be made in accordance with the object to be cleaned. Wherein after
the CO.sub.2 and the impurity pollutants are discharged, another
cleaning can be performed on the object to be cleaned by fresh
CO.sub.2, and the object to be cleaned can be taken out after this
another cleaning.
[0012] The above supercritical CO.sub.2 cleaning system and method
has the advantages of increasing the cleaning efficiency and
shortening the cleaning time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional view of a supercritical CO.sub.2
cleaning system according to the present invention.
[0014] FIG. 2 is a flow chart of a supercritical CO.sub.2 cleaning
method according to the present invention.
[0015] FIG. 3A to 3D are cross-sectional views of a ultrasonic
convergent nozzle of the supercritical CO.sub.2 cleaning system
according to the present invention.
[0016] FIG. 4A to 4D are top views of a movable nozzle set of the
supercritical CO.sub.2 cleaning system according to the present
invention. FIG. 5 illustrates a diagram for the cleaning principle
of a supercritical CO.sub.2 according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] The inventive supercritical CO.sub.2 cleaning system and
method will be illustrated by detailed description of the
embodiment with reference to accompanying drawings.
[0018] Referring to FIG. 1, a preferred embodiment of the
supercritical CO.sub.2 cleaning system is shown, comprising a
closed high-pressure cleaning trough 30, a bearer platform 70, and
a movable nozzle set 61. The closed high-pressure cleaning trough
30 is a funnel-shaped vessel tapered from top to bottom, such that
a space for the bearer platform 70 which can bear an object to be
cleaned 80 and for the movable nozzle set 61 is provided, in order
to be cleaned by the supercritical CO.sub.2 and facilitate the
deposition of impurity pollutants 90. The bearer platform 70 is
located within the closed high-pressure cleaning trough 30 and
rotated with respect to the object to be cleaned and used for
bearing the object to be cleaned 80. And the movable nozzle set 61
is disposed within the closed high-pressure cleaning trough 30 and
above the bearer platform 70, such that the supercritical CO.sub.2
can clean the object to be cleaned 80 via the movable nozzle set
61.
[0019] At first, an object to be cleaned 80 is put on the bearer
platform 70 within the closed cleaning trough 30. The object to be
cleaned 80, for example, may be a wafer, low-k material, or MEMS
etc. A surface treatment can be performed on the surface at which
the object to be cleaned 80 will solidly contact the bearer
platform 70 in order to increase the contact friction, such that
the object to be cleaned or the wafer 80 can closely contact the
bearer platform 70. Then, fresh CO.sub.2 10 can be introduce into
the closed cleaning trough 30, because a high temperature and high
pressure process has been performed such that the CO.sub.2 10 will
automatically inject into the cleaning trough 30 via the movable
nozzle set 61. At the time for cleaning, a suitable combination of
a co-solvent 20 and a surfactant 21 can also be put into the
cleaning trough 30 to achieve the purpose of shortening the
cleaning time. Furthermore, auxiliary ultrasonic oscillators 50 can
be activated in order to achieve the purposes of shortening the
cleaning time and increasing the cleaning performance.
[0020] The position at which the movable nozzle set 61 is disposed
is determined in accordance with the position of the object to be
cleaned 80. An auxiliary ultrasonic oscillator 50 can be combined
with a movable nozzle 60 as a module and the module formed of an
auxiliary ultrasonic oscillator 50 combined with a movable nozzle
60 can be furthermore combined with the bearer platform 70 by
mounting the module above or beneath the bearer platform 70. When
the object to be cleaned 80 is put on the bearer platform 70 within
the cleaning trough 30, the object to be cleaned 80 will be rotated
with respect to the rotation axis 71 in the cleaning system, in
order to remove the impurity pollutants 90. Moreover, the number of
the nozzles in the movable nozzle set 61 and their respective
positions are configured such that the respective working ranges of
these nozzles will overlap with one another, thereby the whole
cleaning area of the object to be cleaned 80 can be covered. The
movable nozzle set 61 can operate with the ultrasonic oscillators
50 in order to increase the cleaning performance. Similarly, the
number of the ultrasonic oscillators 50 and their respective
positions are configured such that the respective working ranges of
these ultrasonic oscillators 50 will overlap with one another,
thereby the whole cleaning area of the object to be cleaned 80 can
be covered. Referring to FIG. 4A to 4D, the movable nozzle set 61,
even along with the ultrasonic oscillators 50, may have different
arrangements for the same working range, such that the respective
working ranges will overlap with one another, thereby the whole
cleaning area of the object to be cleaned 80 can be covered. The
differences among FIG. 4B and FIG. 4D and FIG. 4A and FIG. 4C are
in that with or without the ultrasonic oscillators 50.
[0021] It is noted that, an ultrasonic oscillator 50 can be
combined with a movable nozzle 60 to form a movable nozzle set 61
in which a connector 52 is disposed on a fixed base 56 and the
oscillator is fixed to the base 56 via a bolt 53, and the connector
52 will connect the oscillator along a high-pressure resisting tube
51. The wires will be embedded within the high-pressure resisting
tube 51 in order to avoid polluting the cleaning process. The
surface of the oscillator is a concave 55, such that when the
movable nozzle set 61 is used for cleaning, referring to FIG. 3A
and FIG. 3B, CO.sub.2 will inject out via the ultrasonic oscillator
50 and will converge on the area to be cleaned 59. Alternatively, a
convergent amplifier 57 tapered from one end to the other end
having a structure like a horn can be used, referring to FIG. 3C
and FIG. 3D. Similarly, CO.sub.2 will inject out via the ultrasonic
oscillator 50 and will converge on the area to be cleaned 59. The
ultrasonic oscillator 50 here can be regarded as an ultrasonic
probe 58 underneath which the convergent amplifier 57 is disposed.
When CO.sub.2 injects out, it will be driven into the convergent
amplifier 57 by the ultrasonic probe 58, such that further
convergence is achieved. As shown in FIG. 4B and FIG. 4D, the
convergent amplifier 57 can have any arrangement, as long as the
desired cleaning area 59 can be covered.
[0022] Referring to FIG. 1 again, during the cleaning process, the
impurity pollutants 90 will be extracted out by CO.sub.2 and leave
the object to be cleaned 80. And then the impurity pollutants 90
will converge on the bottom 31 of the cleaning trough 30 along the
cleaning trough 30. Because the cleaning trough 30 is a
funnel-shaped vessel tapered from top to bottom, such that the
impurity pollutants 90 can easily converge on the bottom 31 of the
cleaning trough. Dirty CO.sub.2 11 and the impurity pollutants 90
can leave the cleaning trough 30 by reducing the pressure, and then
another cleaning can be performed on the object to be cleaned 80 by
fresh CO.sub.2 10, and finally the cleaning operation is completed.
Wherein, dirty CO.sub.2 11 can be recycled by a condenser or after
being condensed into a liquid matter.
[0023] During the operation, the bearer platform 70 may be titled
with respect to the horizontal plane with a suitable angle formed
therebetween, such that the rotation axis 71 can easily rotate and
the impurity pollutants 90 can therefore be easily taken away form
the object to be cleaned 80 and the cleaning time can be shortened.
The ultrasonic oscillators 50 can be disposed above or underneath
the object to be cleaned 80 in order to increase the cleaning
performance. Further, a suitable angle can also be formed between
the movable nozzle set 61 and the object to be cleaned 80 in order
to facilitate the cleaning operation and increase the cleaning
performance. In summary, the operation conditions for CO.sub.2
cleaning of the present invention are as follows: the temperature
is defined between 15.degree. C..about.150.degree. C. and the
pressure is defined between 50.about.250 atm. In order to increase
the cleaning performance, the additional ultrasonic set of the
present invention preferably operates at the frequency range
defined between 0.8 MHz.about.3.5 MHz. Moreover, a thermometer 40
and a pressure gauge 41 can be provided within the cleaning trough
30 in order to monitor the above operation conditions in the
cleaning trough 30. A flow chart 100 for this most preferred
embodiment is shown in FIG. 2.
[0024] In the supercritical CO.sub.2 cleaning system and method of
the present invention, a cleaning device can work in conjunction
with co-solvents or surfactants and micro-emulsification technology
for objects to be cleaned under different processes in order to
achieve the optimum cleaning performance. Because the wafer process
or other sophisticated element processes are developed toward the
dimension of 65 nm, such that current wet cleaning technologies can
not overcome the surface tension under the line width of 65 nm.
Further, a lot of super pure water and chemical solvents are needed
in the wet cleaning technologies. Accordingly, the supercritical
CO.sub.2 cleaning technology is disclosed in the present invention
to remove nanopollutants, it can solve convention problems and is a
potential .left brkt-top.Green Cleaning and Producing
Technology.right brkt-bot..
[0025] Referring to FIG. 5, a diagram for the cleaning principle of
a supercritical CO.sub.2 according to the present invention. In
this embodiment, the critical temperature of CO.sub.2 is
31.1.degree. C., and the critical pressure thereof is 73 atm. An
object to be cleaned can be first put into the closed high-pressure
cleaning trough. Liquid CO.sub.2 in the liquid CO.sub.2 tank is
then pressurized above the critical pressure by a transmitting pump
and heated above the critical temperature by a heater. After
entering the supercritical state, CO.sub.2 will enter the cleaning
system, and the pollutants can be removed by the properties of low
surface tension and high permeability of CO.sub.2. It is noted that
the present invention decompresses the supercritical CO.sub.2
containing pollutants through a decompression valve and heavier
pollutants will be deposited at the bottom of the trough after the
decompression. The pollutants can be collected by an absorbing and
filtering apparatus. After a proper treatment, the filtered
CO.sub.2 will become a liquid matter by a condenser or after being
condensed and enter the CO.sub.2 tank for recycling or being
discharged.
[0026] It is to be understood that the foregoing general
description is exemplary and explanatory only and is not
restrictive of the invention as claimed. Various equivalent
alterations and modifications can be made without departing from
the spirit of the present invention and are within the scope of the
following claims.
* * * * *